It's a beautiful small
It's in slightly rough condition - the shell gold is wearing off and there's only a few decorated initials and some line fillers. The hand is a beautiful clear secretary hand, that manages to look big and easy to read, even when you know the lines are only 1/4" high.
The nifty part for me, though, is that Jane wrote across the bottom of several pages - looks like a note to her jailer in the Tower, before she gave the book to him. It goes from 74v - 80r.
She is close in age to Elizabeth I, and would have had a similar 'Renaissance' education, and her hand is very clearly Italic in style, similar to Elizabeth's own hand.
We sometimes think that hands follow each other in sequence, with the old style coming to a screeching halt somehow when a new one arrives.
This is a great illustration that more than one style can share the same place in time; that the noble youth were being taught the newfangled style from Italy, though the secretary bookhand was still in style. BUT: the book decoration is very much 'Renaissance' with the big initials looking three-dimensional and decorated after the Italian style.
ETA: a psalter is a book of the Psalms, which is one of the books of the Bible. This book is actually not psalms from the Bible but devotional prayers in English, written for the new audience of English Christians who followed the 'reforms' of Henry VIII rather than the 'old church'. Sorry for that confusion!